1. Field of the Invention
The present invention relates to an imaging apparatus on which an accessory can be mounted and which can communicate with the accessory, and the accessory which can be mounted on the imaging apparatus.
2. Description of the Related Art
In recent years, in a lens interchangeable camera, a moving image capturing mode has begun to be added in addition to a still image capturing mode. The camera includes not only a type of observing an imaging object using an observation optical system including a reflex mirror but also a type of observing a captured image by displaying the image on a liquid crystal screen for a monitor.
Conventionally, as a system for detecting a focus during moving image capturing and during live view display, a wobbling system for slightly driving a focus lens back and forth (a wobbling operation) to detect a focus has been known in a video camera or the like. In the wobbling system, an automatic focus (AF) evaluation value is taken in while the focus lens is being slightly driven, to determine whether an object is currently in focus. Japanese Patent Application Laid-Open No. 9-284632 discusses a technique for bringing an object into focus using a wobbling system.
During moving image capturing and during preview display, actuators in an interchangeable lens are required to be continuously operated, for example, subjected to focusing and diaphragm driving. Therefore, it is important to control driving of the actuators while frequently monitoring states of the focus lens and a diaphragm. The monitoring of a state of the interchangeable lens and the driving control of each of the actuators are implemented by a communication function between the interchangeable lens and a camera body.
During preview display and during moving image capturing, information relating to the above-mentioned driving control is communicated between a lens microcomputer in the interchangeable lens and a camera microcomputer in the camera body for each frame. Therefore, necessary information is required to be timely communicated to the lens microcomputer and the camera microcomputer. As the camera and the interchangeable lens increase in performance, an amount of data to be communicated increases. Therefore, a communication performance is required to be improved. Japanese Patent Application Laid-Open No. 2009-258558 discusses a camera system including a plurality of communication systems. More specifically, it discusses performing communication using two types of communication systems, i.e., high-speed communication from a lens to a camera and low-speed communication from the camera to the lens during moving image capturing to increase communication efficiency.
During the wobbling operation, storage of charge and driving of the diaphragm for acquiring the AF evaluation value may be desirably performed while the driving of the focus lens is stopped. Because, when the storage of the charge and the driving of the diaphragm for acquiring the AF evaluation value are performed while the focus lens is being driven, the AF evaluation value varies, so that an accurate focusing result is not obtained. Therefore, the camera microcomputer is required to communicate a signal, which is synchronized with exposure of an image sensor, to the lens microcomputer to notify the lens microcomputer of a timing of the exposure of the image sensor in each frame. The camera microcomputer transmits such a signal to the lens microcomputer, so that the lens microcomputer can control a timing of the driving of the focus lens based on the timing of the exposure of the image sensor. As a result, the camera microcomputer can drive the diaphragm and acquire the AF evaluation value while the driving of the focus lens is stopped. However, in the conventional technique, a dedicated signal line is required between the camera and the lens to communicate the signal to the lens microcomputer, leading to an increase in the number of contacts.